Apparatus to measure yarn tension

ABSTRACT

Apparatus to cause a running length of yarn to vibrate at its harmonic frequency and to electronically measure the harmonic frequency thereof to provide a signal which can be employed to maintain and/or correct the parameters of the system to maintain a desired tension in the yarn being run.

This is a division of application Ser. No. 236,966, filed Feb. 23, 1981,now U.S. Pat. No. 4,393,725.

In most textile operations wherein a running strand of yarn is eitherproduced, modified or fabricated, it is advantageous to maintain aconstant yarn tension because variations in yarn tension cause unwantedeffects in the yarn or the fabric being produced therefrom.

Therefore, it is an object of the invention to provide a novel apparatusto measure the tension and/or variations in the tension of a yarn as itruns continuously without physically touching the yarn.

Other objects of the invention will become readily apparent as thespecification proceeds to describe the invention with reference to theaccompanying drawing, in which:

FIG. 1 is a schematic representation of a false twist yarn processemploying the novel yarn tension variation detector, and

FIG. 2 is a perspective view of the specific device to detect yarntension variations.

Looking now to the drawings, the yarn tension variation detector 10 isemployed between the yarn delivery rolls 12, 14 and the draw rolls 16,18 of a false twist yarn producing system. In conventional manner amulti-filament, continuous, fully oriented or partially orientedsynthetic yarn 19 is supplied from a supply package 20 to the falsetwist device 22 through a primary heater 24 by the rolls 12, 14. Fromthe false twist device 22, the false twisted yarn is delivered by thedraw rolls 16, 18 and take-up feed rolls 26, 28 to the take-up package30 through the secondary heater 32. The false twist device 22 can be anysuitable device such as friction discs, pin twister or belt-type.

The yarn tension variation detector 10 basically employs air underpressure to vibrate the yarn 19 at its harmonic frequency and employs aninfra-red photo detector to measure harmonic frequency of the yarn. Achange in the harmonic frequency of the vibrating yarn indicates achange in the yarn tension. The signal from the infra-red detector canbe delivered to a read-out device, such as a counter, and an operatorcan make a manual change in the system or the signal can be supplied toan automatic device which can automatically change roll speeds, etc. tomaintain the desired tension on the yarn.

The yarn tension variation detector 10 can be a single unit for a singleend of yarn 19 or be a multiple unit for multiple ends of yarn 19, asshown in FIG. 2. Each unit 10 is enclosed by a substantially U-shapedframe having upstanding end plates 34 and 36 with notches 38 and 40,respectively, therein. Mounted around or in each of the notches 38 and40 are replaceable ceramic guides 42 and 44, the opening thereof of asize to accommodate a particular range of yarn diameters or devices.

As indicated in FIG. 2, the yarn 19 passes through the detector 10 inthe direction indicated by the arrows. As the yarn passes through thedetector, it passes over an air jet 46, receiving air from the manifold47, whereat the yarn 19 is vibrated by impingement thereon of air fromthe jet 46. Located downstream of the jet 46 is an infra-red photodetector 48 through which the yarn passes to the ceramic guide 44. Theinfra-red photo detector 48 measures the frequency of vibration of theyarn 19 and generates a signal. This signal can be transmitted to theappropriate automatic response device by connection to one or more ofthe electrical tops 50 mounted on the cantilevered detector supportplate 52. The position of the plate 52 can be adjusted to properlylocate the detector 48 relative to the yarn 19 by adjustment of thescrew 54 in cooperation with the spring 56. The position of the air jet46 can also be adjusted by adjustment of the screw 58.

OPERATION

The invention described is predicated on the fact that a yarn stretchedto certain tension and having a certain length will have a certainharmonic frequency. Then, if the tension of a certain pre-determinedlength of yarn changes, the harmonic frequency will change. By measuringthe harmonic frequency of the vibrating yarn 19, the tension and/orchanges of tension in a yarn can be detected. The first naturalfrequency of a yarn can be found by the following formula: ##EQU1##where L=length in meters

T=tension in grams

rho=mass per unit length (gms/meter)

The tension or changes can be computed by measuring the frequency of thevibrating yarn and using the above formula to compute the tension.

In operation, the length of yarn between the guides 42 and 44 and theair from jet 46 is directed against the yarn to cause the yarn 19 to bevibrated at its harmonic frequency. Then as the yarn 19 passes detector48, the frequency is measured and the signal generated thereby isdelivered to a counter or other suitable device. The counter or othersuitable device can be calibrated electronically to incorporate theabove formula to provide a direct reading or response to the measuredfrequency. In this manner, the tension in the yarn 19 is continuouslymonitored and can be maintained at a substantially constant value.

Although the specific embodiment of the invention has been described, itis contemplated that changes can be made without departing from thescope or spirit of the invention and I desire to be limited only by thescope of the claims.

I claim:
 1. Apparatus to provide a false twisted continuous filament,synthetic yarn comprising: a yarn supply means, a false twist mechanism,a primary heater means between said yarn supply means and said falsetwist mechanism, a yarn take-up means, a secondary heater means betweensaid false twist mechanism means and said yarn take-up means and a meansto measure the tension of the yarn being supplied from said yarn supplymeans, said means including a means to vibrate the yarn at its harmonicfrequency and a means to measure the harmonic frequency of the yarn. 2.The apparatus of claim 1 wherein said means to measure the tension ofthe yarn includes a frame, at least one pair of guide members attachedto said frame and longitudinally spaced from one another and said airjet means and said means to measure are located adjacent one anotherbetween said pair of spaced guide members.